“Whether it is the red stripe of Peru, River Plate or Rayo Vallecano, the diagonal sash — in all its forms and colourways — is fundamental to football kit heritage. But where does it come from and who started the trend? That depends on who you ask. In their early days, football shirts were completely plain, so to distinguish two opposing teams, it is believed that a sash band was first introduced as a tool for players to differentiate between team-mates and the opposition. …”
NY Times/The Athletic
A History of Football Kit Design in England and Scotland

Peru, pictured at the 1936 Olympics, are classic purveyors of sashed shirts